FinFET device and method of forming same

ABSTRACT

A method for forming a semiconductor device includes forming a fin over a substrate, forming an isolation region adjacent the fin, forming a dummy gate structure over the fin, recessing the fin adjacent the dummy gate structure to form a first recess using a first etching process, reshaping the first recess to form a reshaped first recess using a second etching process, wherein the second etching process etches upper portions of the fin adjacent the top of the recess more than the second etching process etches lower portions of the fin adjacent the bottom of the recess, and epitaxially growing a source/drain region in the reshaped first recess. Reshaping the first recess includes performing an oxide etch process, wherein the oxide etch process forms a porous material layer within the recess.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims the benefit of U.S. Provisional Application No.62/552,967, “FinFET Device and Method of Forming Same” filed on Aug. 31,2017, which application is hereby incorporated herein by reference.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as, for example, personal computers, cell phones, digital cameras,and other electronic equipment. Semiconductor devices are typicallyfabricated by sequentially depositing insulating or dielectric layers,conductive layers, and semiconductor layers of material over asemiconductor substrate, and patterning the various material layersusing lithography to form circuit components and elements thereon.

The semiconductor industry continues to improve the integration densityof various electronic components (e.g., transistors, diodes, resistors,capacitors, etc.) by continual reductions in minimum feature size, whichallow more components to be integrated into a given area. However, asthe minimum features sizes are reduced, additional problems arise thatshould be addressed.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a perspective view of a fin field-effect transistor (“FinFET”)device in accordance with some embodiments.

FIG. 2A is a cross-sectional view of an intermediate stage in themanufacture of a FinFET device in accordance with some embodiments.

FIG. 3A is a cross-sectional view of an intermediate stage in themanufacture of a FinFET device in accordance with some embodiments.

FIG. 4A is a cross-sectional view of an intermediate stage in themanufacture of a FinFET device in accordance with some embodiments.

FIG. 5A is a cross-sectional view of an intermediate stage in themanufacture of a FinFET device in accordance with some embodiments.

FIGS. 6A-6B are cross-sectional views of intermediate stages in themanufacture of a FinFET device in accordance with some embodiments.

FIGS. 7A-7C are cross-sectional views of intermediate stages in themanufacture of a FinFET device in accordance with some embodiments.

FIGS. 8A-8C are cross-sectional views of intermediate stages in themanufacture of a FinFET device in accordance with some embodiments.

FIGS. 9A-9C are cross-sectional views of intermediate stages in themanufacture of a FinFET device in accordance with some embodiments.

FIGS. 10A-10F are cross-sectional views of recess etching in themanufacture of a FinFET device in accordance with some embodiments.

FIGS. 11A-11C are cross-sectional views of intermediate stages in themanufacture of a FinFET device in accordance with some embodiments.

FIGS. 12A-12C are cross-sectional views of intermediate stages in themanufacture of a FinFET device in accordance with some embodiments.

FIGS. 13A-13C are cross-sectional views of intermediate stages in themanufacture of a FinFET device in accordance with some embodiments.

FIGS. 14A-14C are cross-sectional views of intermediate stages in themanufacture of a FinFET device in accordance with some embodiments.

FIGS. 15A-15C are cross-sectional views of intermediate stages in themanufacture of a FinFET device in accordance with some embodiments.

FIGS. 16A-16C are cross-sectional views of intermediate stages in themanufacture of a FinFET device in accordance with some embodiments.

FIGS. 17A-17C are cross-sectional views of intermediate stages in themanufacture of a FinFET device in accordance with some embodiments.

FIG. 18 is a flow diagram illustrating a method of forming a FinFETdevice in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Embodiments will be described with respect to a specific context,namely, a FinFET device and a method of forming the same. Variousembodiments discussed herein allow for controlling the shape of achannel region of a FinFET device, such that the top of the channelregion is reduced in size more than the middle of the channel region isreduced in size or more than a height of the channel region isincreased. By controlling the shape of the channel region of a FinFET inthis manner, the performance of the FinFET device may be improved.Various embodiments presented herein are discussed in the context ofFinFETs formed using a gate-last process. In other embodiments, agate-first process may be used. Some embodiments contemplate aspectsused in planar devices, such as planar FETs. Some embodiments may beused in a device such as a ring oscillator, or may be used in othertypes of devices. Some embodiments may also be used in semiconductordevices other than FETs.

FIG. 1 illustrates an example of a fin field-effect transistor (FinFET)30 in a three-dimensional view. The FinFET 30 comprises a fin 36 on asubstrate 32. The substrate 32 includes isolation regions 34, and thefin 36 protrudes above and from between neighboring isolation regions34. A gate dielectric 38 is along sidewalls and over a top surface ofthe fin 36, and a gate electrode 40 is over the gate dielectric 38.Source/drain regions 42 and 44 are disposed in opposite sides of the fin36 with respect to the gate dielectric 38 and gate electrode 40. FIG. 1further illustrates reference cross-sections that are used in subsequentfigures. Cross-section A-A is across a channel, gate dielectric 38, andgate electrode 40 of the FinFET 30. Cross-section C-C is in a plane thatis parallel to cross-section A-A and is across fin 36 outside of thechannel. Cross-section B-B is perpendicular to cross-section A-A and isalong a longitudinal axis of the fin 36 and in a direction of, forexample, a current flow between the source/drain regions 42 and 44.Subsequent figures refer to these reference cross-sections for clarity.

FIGS. 2A through 17C are cross-sectional views of intermediate stages inthe manufacturing of FinFETs in accordance with some embodiment. InFIGS. 2A through 9A-C and FIGS. 11A-C through 17A-C, figures ending withan “A” designation are illustrated along the reference cross-section A-Aillustrated in FIG. 1, except for multiple FinFETs and multiple fins perFinFET. Figures ending with a “B” designation are illustrated along thereference cross-section B-B illustrated in FIG. 1. Figures ending with a“C” designation are illustrated along the cross-section C-C illustratedin FIG. 1. FIGS. 10A-F are all illustrated along the referencecross-section B-B illustrated in FIG. 1.

FIG. 2A illustrates a substrate 50. The substrate 50 may be asemiconductor substrate, such as a bulk semiconductor, asemiconductor-on-insulator (SOI) substrate, or the like, which may bedoped (e.g., with a p-type or an n-type dopant) or undoped. Thesubstrate 50 may be a wafer, such as a silicon wafer. Generally, an SOIsubstrate comprises a layer of a semiconductor material formed on aninsulator layer. The insulator layer may be, for example, a buried oxide(BOX) layer, a silicon oxide layer, or the like. The insulator layer isprovided on a substrate, typically a silicon substrate or a glasssubstrate. Other substrates, such as a multi-layered or gradientsubstrate may also be used. In some embodiments, the semiconductormaterial of the substrate 50 may include silicon; germanium; a compoundsemiconductor including silicon carbide, gallium arsenic, galliumphosphide, indium phosphide, indium arsenide, and/or indium antimonide;an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs,GaInP, and/or GaInAsP; or combinations thereof.

The substrate 50 may further include integrated circuit devices (notshown). As one of ordinary skill in the art will recognize, a widevariety of integrated circuit devices such as transistors, diodes,capacitors, resistors, the like, or combinations thereof may be formedin and/or on the substrate 50 to generate the structural and functionalrequirements of the design for the resulting FinFETs. The integratedcircuit devices may be formed using any suitable methods.

In some embodiments, the substrate 50 may comprise a first region 100Aand a second region 100B. The first region 100A can be for formingn-type devices, such as NMOS transistors, such as n-type FinFETs. Thesecond region 100B can be for forming p-type devices, such as PMOStransistors, such as p-type FinFETs. Accordingly, the first region 100Amay be also referred to as an NMOS region 100A, and the second region100B may be also referred to as a PMOS region 100B. In some embodiments,the first region 100A may be physically separated from the second region100B. The first region 100A may be separated from the second region 100Bby any number of features.

FIG. 2A further illustrates the formation of a mask 53 over thesubstrate 50. In some embodiments, the mask 53 may be used in asubsequent etching step to pattern the substrate 50 (See FIG. 3A). Asshown in FIG. 2A, the mask 53 may include a first mask layer 53A and asecond mask layer 53B. The first mask layer 53A may be a hard masklayer, may comprise silicon nitride, silicon oxynitride, siliconcarbide, silicon carbonitride, a combination thereof, or the like, andmay be formed using any suitable process, such as atomic layerdeposition (ALD), physical vapor deposition (PVD), chemical vapordeposition (CVD), a combination thereof, or the like. The first masklayer 53A may also include multiple layers, and the multiple layers maybe different materials. For example, the first mask layer 53A mayinclude a layer of silicon nitride over a layer of silicon oxide, thoughother materials and combinations of materials may also be used. Thesecond mask layer 53B may comprise photoresist, and in some embodiments,may be used to pattern the first mask layer 53A for use in thesubsequent etching step discussed above. The second mask layer 53B maybe formed by using a spin-on technique and may be patterned usingacceptable photolithography techniques. In some embodiments, the mask 53may comprise three or more mask layers.

FIG. 3A illustrates the formation of semiconductor strips 52 in thesubstrate 50. First, mask layers 53A and 53B may be patterned, whereopenings in mask layers 53A and 53B expose areas 55 of the substrate 50where Shallow Trench Isolation (STI) regions 54 will be formed. Next, anetching process may be performed, where the etching process creates thetrenches 55 in the substrate 50 through the openings in the mask 53. Theremaining portions of the substrate 50 underlying a patterned mask 53form a plurality of semiconductor strips 52. The etching may be anyacceptable etch process, such as a reactive ion etch (RIE), neutral beametch (NBE), the like, or a combination thereof. The etch process may beanisotropic. In some embodiments, the semiconductor strips 52 may have aheight H₁ between about 200 nm and about 400 nm, and may have a width W₁between about 10 nm and about 40 nm.

The semiconductor strips 52 may be patterned by any suitable method. Forexample, the semiconductor strips 52 may be patterned using one or morephotolithography processes, including double-patterning ormulti-patterning processes. Generally, double-patterning ormulti-patterning processes combine photolithography and self-alignedprocesses, allowing patterns to be created that have, for example,pitches smaller than what is otherwise obtainable using a single, directphotolithography process. For example, in one embodiment, a sacrificiallayer is formed over substrate 50 and patterned using a photolithographyprocess. Spacers may be formed alongside the patterned sacrificial layerusing a self-aligned process. The sacrificial layer is then removed, andthe remaining spacers, or mandrels, may then be used as a mask topattern the semiconductor strips 52.

FIG. 4A illustrates the formation of an insulation material in thetrenches 55 (see FIG. 3A) between neighboring semiconductor strips 52 toform isolation regions 54. The insulation material may be an oxide, suchas silicon oxide, a nitride, such as silicon nitride, the like, or acombination thereof, and may be formed by a high density plasma chemicalvapor deposition (HDP-CVD), a flowable CVD (FCVD) (e.g., a CVD-basedmaterial deposition in a remote plasma system and post curing to make itconvert to another material, such as an oxide), the like, or acombination thereof. Other insulation materials formed by any acceptableprocesses may be also used.

Furthermore, in some embodiments, the isolation regions 54 may include aconformal liner (not illustrated) formed on sidewalls and a bottomsurface of the trenches 55 (see FIG. 3A) prior to the filling of thetrenches 55 with an insulation material of the isolation regions 54. Insome embodiments, the liner may comprise a semiconductor (e.g., silicon)nitride, a semiconductor (e.g., silicon) oxide, a thermal semiconductor(e.g., silicon) oxide, a semiconductor (e.g., silicon) oxynitride, apolymer dielectric, combinations thereof, or the like. The formation ofthe liner may include any suitable method, such as ALD, CVD, HDP-CVD,PVD, a combination thereof, or the like. In such embodiments, the linermay prevent (or at least reduce) the diffusion of the semiconductormaterial from the semiconductor strips 52 (e.g., Si and/or Ge) into thesurrounding isolation regions 54 during the subsequent annealing of theisolation regions 54. For example, after the insulation material of theisolation regions 54 are deposited, an annealing process may beperformed on the insulation material of the isolation regions 54.

Referring further to FIG. 4A, a planarization process, such as achemical mechanical polishing (CMP), may remove any excess insulationmaterial of the isolation regions 54, such that top surfaces of theisolation regions 54 and top surfaces of the semiconductor strips 52 arecoplanar. In some embodiments, the CMP may also remove the mask 53. Inother embodiments, the mask 53 may be removed using a wet etchingprocess separate from the CMP.

FIG. 5A illustrates the recessing of the isolation regions 54 to formfins 56. The isolation regions 54 are recessed such that fins 56 in thefirst region 100A and in the second region 100B protrude from betweenneighboring isolation regions 54. In some embodiments, the semiconductorstrips 52 may be considered to be part of the fins 56. Further, the topsurfaces of the isolation regions 54 may have a flat surface asillustrated, a convex surface, a concave surface (such as dishing), or acombination thereof. The top surfaces of the isolation regions 54 may beformed flat, convex, and/or concave by an appropriate process. Theisolation regions 54 may be recessed using an acceptable etchingprocess, such as one that is selective to the material of the isolationregions 54. For example, a STI oxide removal using a CERTAS® etch, anApplied Materials SICONI or R2 tool, or dilute hydrofluoric (dHF) acidmay be used.

A person having ordinary skill in the art will readily understand thatthe process described with respect to FIGS. 2A through 5A is just oneexample of how the fins 56 may be formed. In other embodiments, adielectric layer can be formed over a top surface of the substrate 50;trenches can be etched through the dielectric layer; homoepitaxialstructures can be epitaxially grown in the trenches; and the dielectriclayer can be recessed such that the homoepitaxial structures protrudefrom the dielectric layer to form fins. In yet other embodiments,heteroepitaxial structures can be used for the fins. For example, thesemiconductor strips 52 in FIG. 4A can be recessed, and a materialdifferent from the semiconductor strips 52 may be epitaxially grown intheir place. In even further embodiments, a dielectric layer can beformed over a top surface of the substrate 50; trenches can be etchedthrough the dielectric layer; heteroepitaxial structures can beepitaxially grown in the trenches using a material different from thesubstrate 50; and the dielectric layer can be recessed such that theheteroepitaxial structures protrude from the dielectric layer to formfins 56. In some embodiments where homoepitaxial or heteroepitaxialstructures are epitaxially grown, the grown materials may be in situdoped during growth. In other embodiments, homoepitaxial orheteroepitaxial structures may be doped using, for example, ionimplantation after homoepitaxial or heteroepitaxial structures areepitaxially grown. Still further, it may be advantageous to epitaxiallygrow a material in the NMOS region 100A different from the material inthe PMOS region 100B. In various embodiments, the fins 56 may comprisesilicon germanium (Si_(x)Ge_(1-x), where x can be between approximately0 and 1), silicon carbide, pure or substantially pure germanium, a III-Vcompound semiconductor, a II-VI compound semiconductor, or the like. Forexample, the available materials for forming III-V compoundsemiconductor include, but are not limited to, InAs, AlAs, GaAs, InP,GaN, InGaAs, InAlAs, GaSb, AlSb, AlP, GaP, and the like.

In FIGS. 6A and 6B, a dummy dielectric layer 58 is formed on the fins56. The dummy dielectric layer 58 may be, for example, silicon oxide,silicon nitride, a combination thereof, or the like, and may bedeposited (using, for example, CVD, PVD, a combination thereof, or thelike) or thermally grown (for example, using thermal oxidation, or thelike) according to acceptable techniques. A dummy gate layer 60 isformed over the dummy dielectric layer 58, and a mask 62 is formed overthe dummy gate layer 60. In some embodiments, the dummy gate layer 60may be deposited over the dummy dielectric layer 58 and then planarizedusing, for example, a CMP process. The mask 62 may be deposited over thedummy gate layer 60. The dummy gate layer 60 may be made of, forexample, polysilicon, although other materials that have a high etchingselectivity with respect to the material of the isolation regions 54 mayalso be used. The mask 62 may include one or more layers of, forexample, silicon nitride, silicon oxynitride, silicon carbide, siliconcarbonitride, the like, or a combination thereof.

Referring further to FIGS. 6A and 6B, in the illustrated embodiment, asingle dummy dielectric layer 58, a single dummy gate layer 60, and asingle mask 62 are formed across the first region 100A and the secondregion 100B. In other embodiments, separate dummy dielectric layers,separate dummy gate layers, and separate masks may be formed in thefirst region 100A and the second region 100B. In some embodiments, thedummy dielectric layer 58 may have a thickness between about 0.8 nm andabout 2.0 nm, and the dummy gate layer 60 may have a thickness betweenabout 50 nm and about 100 nm.

In FIGS. 7A, 7B, and 7C, the mask 62 (see FIGS. 6A and 6B) may bepatterned using acceptable photolithography and etching techniques toform a mask 72 in the first region 100A and in the second region 100B.The mask 72 may be a hardmask, and the pattern of the mask 72 may bedifferent between the first region 100A and the second region 100B Thepattern of the mask 72 may be transferred to the dummy gate layer 60 byan acceptable etching technique to form dummy gate stack 70 in the firstregion 100A and in the second region 100B. The dummy gate stack 70includes the dummy gate layer 60 and the mask 72. In some embodiments,the dummy gate layer 60 and the mask 72 are formed in separate processesin the first region 100A and the second region 100B, and may be formedof different materials in the first region 100A and the second region100B. Optionally, the pattern of the mask 72 may similarly betransferred to dummy dielectric layer 58. The pattern of the dummy gatestack 70 covers respective channel regions of the fins 56 while exposingsource/drain regions of the fins 56. The dummy gate stack 70 may alsohave a lengthwise direction substantially perpendicular to thelengthwise direction of respective fins 56. A size of the dummy gatestack 70 or a pitch between dummy gate stacks 70 may depend on a regionof a die in which the dummy gates are formed. In some embodiments, dummygate stacks 70 may have a larger size or a larger pitch when located inan input/output region of a die (e.g., where input/output circuitry isdisposed) than when located in a logic region of a die (e.g., wherelogic circuitry is disposed). In some embodiments, the dummy gate stacks70 may have a width between about 15 nm and about 40 nm.

Referring further to FIGS. 7A, 7B and 7C, appropriate wells (not shown)may be formed in the fins 56, the semiconductor strips 52, and/or thesubstrate 50. For example, a P-well may be formed in the first region100A, and an N-well may be formed in the second region 100B. Thedifferent implant steps for the different regions 100A and 100B may beachieved using a photoresist or other masks (not shown). For example, aphotoresist is formed over the fins 56 and the isolation regions 54 inthe first region 100A and the second region 100B. The photoresist ispatterned to expose the second region 100B of the substrate 50, such asa PMOS region, while protecting the first region 100A, such as an NMOSregion. The photoresist can be formed by using a spin-on technique andcan be patterned using acceptable photolithography techniques. Once thephotoresist is patterned, n-type impurities are implanted in the secondregion 100B, and the photoresist may act as a mask to substantiallyprevent n-type impurities from being implanted into the first region100A. The n-type impurities may be phosphorus, arsenic, or the like, andmay be implanted in the second region 100B to a concentration of equalto or less than 10¹⁸ cm⁻³, such as in a range from about 10¹⁷ cm⁻³ toabout 10¹⁸ cm⁻³. After the implantation process, the photoresist isremoved using, for example, an acceptable ashing process followed by awet cleaning process.

Following the implanting of the second region 100B, a second photoresist(not shown) is formed over the fins 56 and the isolation regions 54 inthe first region 100A and the second region 100B. The second photoresistis patterned to expose the first region 100A of the substrate 50, whileprotecting the second region 100B. The second photoresist can be formedby using a spin-on technique and can be patterned using acceptablephotolithography techniques. Once the second photoresist is patterned,p-type impurities are implanted in the first region 100A, and the secondphotoresist may act as a mask to substantially prevent p-type impuritiesfrom being implanted into the second region 100B. The p-type impuritiesmay be boron, BF₂, or the like, and may be implanted in the first region100A to a concentration of equal to or less than 10¹⁸ cm⁻³, such as in arange from about 10¹⁷ cm⁻³ to about 10¹⁸ cm⁻³. After the implantationprocess, the second photoresist is removed using, for example, anacceptable ashing process followed by a wet cleaning process.

After implanting appropriate impurities in first region 100A and thesecond region 100B, an anneal may be performed to activate the p-typeand n-type impurities that were implanted. The implantation process mayform a P-well in the first region 100A, and an N-well in the secondregion 100B. In some embodiments where the fins are epitaxial grown, thegrown materials of the fins 56 may be in situ doped during the growthprocess.

In FIGS. 8A, 8B, and 8C, a gate spacer layer 80 is formed on exposedsurfaces of the dummy gate stacks 70 (see FIGS. 8A and 8B) and/or thedummy dielectric layer 58 over the fins 56 (see FIG. 8C). Any suitablemethods of forming the gate spacer layer 80 may be used. In someembodiments, a deposition (such as CVD, ALD, or the like) may be usedform the gate spacer layer 80. In some embodiments, the gate spacerlayer 80 may include one or more layers of, for example, silicon nitride(SiN), silicon oxynitride, silicon carbonitride, silicon oxycarbonitride(SiOCN), a combination thereof, or the like.

Referring further to FIGS. 8A, 8B, and 8C, lightly doped source/drain(LDD) regions 75 and 79 may be formed in the substrate 50 in the firstregion 100A and the second region 100B, respectively. Similar to theimplantation process discussed above with reference to FIGS. 7A, 7B and7C, a mask (not shown), such as a photoresist, may be formed over thefirst region 100A, e.g., the NMOS region, while exposing the secondregion 100B, e.g., the PMOS region, and p-type impurities may beimplanted into the exposed fins 56 in the second region 100B to createLDD regions 79. During the implantation of the LDD regions 79, the dummygate 70 may act as a mask to prevent (or at least reduce) dopants fromimplanting into a channel region of the exposed fins 56. Thus, the LDDregions 79 may be formed substantially in source/drain regions of theexposed fins 56. The mask may then be removed. Subsequently, a secondmask (not shown), such as a photoresist, may be formed over the secondregion 100B, while exposing the first region 100A, and n-type impuritiesmay be implanted into the exposed fins 56 in the first region 100A tocreate LDD regions 75. During the implantation of the LDD regions 75,the dummy gate stack 70 may act as a mask to prevent (or at leastreduce) dopants from implanting into a channel region of the exposedfins 56. Thus, the LDD regions 75 may be formed substantially insource/drain regions of the exposed fins 56. The second mask may then beremoved. The n-type impurities may be any of the n-type impuritiespreviously discussed, and the p-type impurities may be any of the p-typeimpurities previously discussed. The LDD regions 75 and 79 may each havea concentration of impurities from about 10¹⁵ cm⁻³ to about 10¹⁶ cm⁻³.An annealing process may be performed to activate the implantedimpurities.

Referring to FIGS. 9A, 9B, and 9C, an etching process is performed onportions of the gate spacer layer 80. The etching process may beanisotropic. After preforming the etching process, lateral portions ofthe spacer layer over the LDD regions 75 and over the isolation regions54 may be removed to expose top surfaces of the fins 56 and the masks 72for the dummy gate stack 70. Portions of the spacer layer 80 alongsidewalls of the dummy gate stack 70 may remain to form gate spacers 122and along sidewalls of the fins 56 may remain to form fin spacers 130.In other embodiments, the spacer layer 80 may also be removed from thesidewalls of the fins 56. In some embodiments, the spacer layer 80 inthe second region 100B is also patterned to form gate spacers 122 andfin spacers 130 along sidewalls of the dummy gates 70 and the fins 56.In some embodiments, gate spacers 122 and fin spacers 130 are formed atthe same time in first region 100A and second region 100B, and in otherembodiments, gate spacers 122 and fin spacers 130 are formed in aseparate process in first region 100A and second region 100B.

FIGS. 10A through 12C illustrate the formation of epitaxial source/drainregions 82 and 84 in the first region 100A and the second region 100B.In some embodiments, the epitaxial source/drain regions 82 (see FIGS.12B and 12C) in the first region 100A may be formed before the epitaxialsource/drain regions 84 (see FIGS. 12B and 12C) are formed in the secondregion 100B. In other embodiments, the epitaxial source/drain regions 84in the second region 100B may be formed before forming the epitaxialsource/drain regions 82 in first region 100A.

FIGS. 10A through 12C illustrate the formation of the epitaxialsource/drain regions 82 in the first region 100A between neighboringfins 56. FIGS. 10A-10F are all illustrated along the referencecross-section B-B illustrated in FIG. 1. During the formation of theepitaxial source/drain regions 82 in first region 100A, e.g., the NMOSregion, the second region 100B, e.g., the PMOS region may be masked (notshown). Referring first to FIG. 10A, a patterning process is performedon the fins 56 to form recesses 126 in source/drain regions of the fins56. The first patterning process may be performed in a manner that therecesses 126 are formed between neighboring dummy gate stacks 70 (ininterior regions of the fins 56), or between an isolation region 54 andadjacent dummy gate stacks 70 (in end regions of the fins 56) as shownin the cross-section illustrated later in FIG. 11B. In some embodiments,the patterning process may include a suitable anisotropic dry etchingprocess, while using the dummy gate stacks 70, the gate spacers 122, thefin spacers 130 and/or isolation regions 54 as a combined mask. Thesuitable anisotropic dry etching process may include a reactive ion etch(RIE), neutral beam etch (NBE), the like, or a combination thereof. Insome embodiments where the RIE is used in the first patterning process,process parameters such as, for example, a process gas mixture, avoltage bias, and an RF power may be chosen such that etching ispredominantly performed using physical etching, such as ion bombardment,rather than chemical etching, such as radical etching through chemicalreactions. In some embodiments, a voltage bias may be increased toincrease energy of ions used in the ion bombardment process and, thus,increase a rate of physical etching. Since, the physical etching inanisotropic in nature and the chemical etching is isotropic in nature,such an etching process has an etch rate in the vertical direction thatis greater than an etch rate in the lateral direction. In someembodiments, the anisotropic etching process may be performed using aprocess gas mixture including CH₃F, CH₄, HBr, O₂, Ar, a combinationthereof, or the like. In some embodiments, the first patterning processforms recesses 126 having U-shaped bottom surfaces 135 a. The recesses126 may also be referred to as U-shaped recesses 126, an example recess126 of which is shown in FIG. 10A. FIG. 10A also shows the recess 126has a surface proximity SP₁, measured laterally from the middle of thedummy gate 60 to the top of the recess 126, and a tip proximity TP₁,measured laterally from the middle of the dummy gate 60 to the edge ofthe recess 126 at half of the depth of the recess 126. In someembodiments, the recess 126 has a trench depth TD₁, as measured from atop surface of the fins 56, between about 40 nm and about 70 nm, such asabout 53 nm. In some embodiments, the etching process for forming theU-shaped recesses 126 may also etch isolation regions, which isillustrated later in FIGS. 11C-17C by dashed lines.

FIG. 10B illustrates the recess 126 after a native oxide 132 has formedon surface of the recess 126 after the patterning process described inFIG. 10A. The native oxide may, for example, be a silicon oxide for anembodiment in which the substrate 50 (and the semiconductor strips 52and the fins 56) are silicon. In some cases, the native oxide 132 mayhave a thickness between about 0.6 nm and about 1.8 nm, such as about1.5 nm. In some cases, the native oxide 132 forms once the substrate 50is removed from a chamber (e.g., a vacuum) in which the patterningprocess is performed.

In some embodiments, the native oxide 132 is removed using a surfacemodification process, which in some embodiments may be a dry etch suchas an RIE process. The surface modification process may use acombination of NF₃ and NH₃ as process gases. Other gases mayadditionally be used in the surface modification process, such as He orAr. During the surface modification process, the NF₃ and NH₃ gases reactwith the silicon oxide 132 to form water and solid ammoniumfluorosilicate (AFS), (NH₄)₂SiF_(x). The reaction can be expressed as:SiO₂+NF₃+NH₃→(NH₄)₂SiF_(x)+H₂O

As shown in FIG. 10C, the AFS 134 is a solid phase byproduct that, whenformed during the surface modification process, can cover the surface ofthe recess 126. In some cases, the AFS 134 may also be present onportions of gate spacers 122, as shown in FIG. 10C. The thickness andextent of the AFS 134 may be controlled by controlling the processconditions of the surface modification process, such as energy,temperature, pressure, amount or flow rate of the process gases, orother conditions. In some cases, the thickness of the AFS 134 formed isbetween about 4-8 times the initial thickness of the native oxide 132.In some cases, the thickness of the AFS 134 material formed on therecess 126 is between about 4 nm and about 8 nm, though in other casesthe AFS 134 may have a different thickness.

In some cases, the AFS 134 can form as a porous material. This porosityallows the AFS 134 to absorb process gases, radicals, reactionbyproducts, etchants, and other materials present during the surfacemodification process. The materials that can be absorbed by the AFS 134are shown collectively in FIG. 10C as initial etchants 136. The initialetchants 136 may be absorbed throughout the AFS 134. The initialetchants 136 may, for example, include NH₃, NF₃, H₂O, radicals such asHF* or F*, or other substances. The amounts, concentrations, or types ofthe initial etchants 136 can be controlled by controlling thecharacteristics of the surface modification process. Examplecharacteristics include process gas flow rate, pressure, the ratio ofthe process gases, or other characteristics. As discussed below, theabsorbed initial etchants 136 can enable additional etching of therecess 126.

FIG. 10D illustrates the recess 126 after an initial pumping stage hasbeen performed to remove portions of the AFS 134. During the initialpumping stage, portions of AFS 134 are pumped out of the recess 126.However, due to the shape and depth of the recess 126, during pumpingthe flow near the bottom surface 135 a of the recess 126 is greater thanthe flow near vertical sidewalls of the recess, such as near the topsurface 135 b of the recess 126. Thus, AFS 134 near the bottom surface135 a is pumped out of the recess 126 more efficiently than AFS 134 nearthe top surface 135 b of the recess. Due to the differences in pumpingefficiency, the initial pumping stage may remove more of the AFS 134present near the bottom surface 135 a of the recess 126 than the AFS 134present near the top surface 135 b of the recess 126. In some cases, theinitial pumping stage removes almost all of the AFS 134 present near thebottom surface 135 a. In some embodiments, the AFS 134 remaining nearthe top surface 135 b may have a thickness between about 4 nm and about8 nm, though the AFS 134 near the top surface 135 b may have anotherthickness in other cases. In some embodiments, the AFS 134 remainingnear the bottom surface 135 a may have a thickness less than about 0.1nm, though the AFS 134 near the bottom surface 135 a may have anotherthickness in other cases. In some cases, during the initial pumpingstage some of the AFS 134 removed near the bottom surface 135 aredeposits near the top surface 135 b. As a result, the AFS 134 near thetop surface 135 b may be thicker than the AFS 134 near the bottomsurface 135 a.

In some embodiments, the amount and distribution of AFS 134 remainingafter the initial pumping stage can be controlled by controlling theconditions of the initial pumping stage. Example initial pumping stageconditions that can be controlled include pressure, duration, andtemperature. In some embodiments, the process pressure during theinitial pumping stage may be between about 100 mTorr and about 700mTorr. In some embodiments, the temperature during the initial pumpingstage may be higher than about 75° C., such as about 90° C.

As described above with respect to FIG. 10C, some initial etchants 136from the surface modification process are absorbed within the AFS 134.Some of the initial etchants 136 absorbed within the AFS 134 can reactwith byproducts also absorbed within the AFS 134 to further etch thesides of the recess 126. FIG. 10E illustrates the AFS 134 as containingsecondary etchants 138 formed from absorbed initial etchants 136, thoughsecondary etchants 138 may form from absorbed initial etchants 136 atany point during or after the surface modification process. Secondaryetchants 138 that diffuse through the AFS 134 to the surface of therecess 126 are able to additionally etch the surface material. Forexample, the secondary etchants 138 may additionally etch material ofthe substrate 50, semiconductor strips 52, or fins 56 present at thesurface of the recess 126. Because the thickest regions of remaining AFS134 are near the top surfaces 135 b of the recess 126, the amount ofsecondary etchants 138 is greatest near the top surfaces 135 b. Thus,surface material near the top surfaces 135 b of the recess 126 isadditionally etched by the secondary etchants 138 more than surfacematerial near the bottom surfaces 135 a of the recess. In some cases,some surfaces of the recess 126 may not be additionally etched bysecondary etchants 138, for example if no AFS 134 is present over thosesurfaces or if AFS 134 is thin over those surfaces. The additionaletching may be isotropic or anisotropic, depending on the specificsecondary etchants 138 present. The additional etching may be performedin the same chamber as the surface modification process or the initialpumping stage.

FIG. 10F illustrates the recess 126 after the secondary etchants 138have additionally etched portions of the surface material and after theAFS 134 has been removed. The AFS 134 is removed during subsequentprocess steps, which are described in greater detail below. As FIG. 10Fshows, the top surfaces 135 b of the recess 126 have been etched morethan the bottom surfaces 135 a of the recess 126. In particular, withreference to FIG. 10A and FIG. 10F, the surface proximity is reducedfrom SP₁ to SP₂ more than the tip proximity is reduced from TP₁ to TP₂and more than the trench depth is increased from TD₁ to TD₂. In someembodiments, the additional etching due to the secondary etchants 138reduces the surface proximity between about 0.5 nm and about 1.5 nm,such as about 1.3 nm. In some embodiments, the additional etchingreduces the tip proximity less than about 1 nm. In some embodiments, theadditional etching increases the trench depth less than about 0.1 nm. Insome cases, the additional etching can increase the diameter of the topof the recess 126 more than the additional etching increases the lateraldiameter of portions of the recess 126 below the top of the recess 126.In some embodiments, the amount and distribution of the additionaletching may be controlled by controlling the surface modificationprocess characteristics or the initial pumping stage characteristics, asdescribed previously. In some cases, the additional etching can giverecess 126 a flared or “trumpet” shape, as showed in in FIG. 10F, thoughin other cases portions of the sides of the recess 126 may be straight.

In some cases, the use of the additional etching as described herein canreduce the amount of process residue or undesired impurities (e.g., C,O, N, Cl, F, or other substances) present on surfaces of the recess 126.For example, in some cases, the additional etching can reduce theconcentration of C impurities by about 28%, the concentration of Oimpurities by about 95%, the concentration of N impurities by about 63%,the concentration of Cl impurities by about 53%, or the concentration ofF impurities by about 33%. In other cases, the additional etching mayreduce different amounts of impurities than these illustrative examples.

By shaping the recess 126, the additional etching of recess 126described in FIGS. 10A-10F also shapes the fins 56. The additionaletching thus can shape the fins 56 such that the top of each fin 56 hasa smaller width between each recess 126, as indicated by the reductionof surface proximity described above. The additional etching can reducethe width of portions of a fin 56 in a region closer to the gate stack(i.e., near the top of the fin 56) more than the additional etchingreduces the width of portions of the fin 56 in a region farther from thegate stack (i.e., near the bottom of the fin 56). In this manner, theadditional etching can increase the tapering of sidewalls of a 56, orincrease the slope of sidewalls of a fin 56, particularly near the topof the fin 56.

One or more secondary etchants 138 may form from absorbed initialetchants 136 within the AFS 134. For example, NH₃ can react with H₂Oalso present in the AFS 134 to form ammonium hydroxide (NH₄OH), which isan etchant of silicon:NH₃+H₂O→NH₄OH.As another example, HF* and F* radicals present in the AFS 134 also canattack silicon according to the reactionHF*+F*+Si→SiF_(x)+SiH*.In some cases, some of the radicals absorbed into the AFS 134 may beelectrically neutral. These example secondary etchants can etch surfacesof a recess formed in a silicon substrate. In some embodiments, othertypes of secondary etchants may be formed that etch silicon. In someembodiments, types of secondary etchants may be formed that etch othertypes of substrates than silicon. In some embodiments, the differenttypes, amounts, relative proportions, or other characteristics of thesecondary etchants may be controlled by controlling the surfacemodification process characteristics or the initial pumping stagecharacteristics, as described previously. In some embodiments, othergases than surface modification process gases may be introduced into thesurface modification process chamber to form etchants within the AFS134. In some cases, the additional etching is self-limited. For example,the additional etching stops after the secondary etchants 138 aredepleted if the absorbed initial etchants 136 or reactive byproducts arenot replenished within the AFS 134. In this manner, the amount ofadditional etching can be controlled by controlling the absorption ofinitial etchants 136 into the AFS 134. For example, the duration ofexposure, the pressure, the flow rate, or the ratio of process gases maybe controlled, though controlling other characteristics may also controlthe amount of initial etchants 136 absorbed or secondary etchants 138created.

After the additional etching due to the secondary etchants 138, a secondpumping stage may be performed to remove the AFS 134 and any othermaterials within the AFS, such as absorbed initial etchants 136,secondary etchants 138, etchant byproducts, etc. In some embodiments,the process pressure during the second pumping stage may be less thanabout 1 mTorr. In some embodiments, the duration of the second pumpingstage may be between about 10 seconds and about 30 seconds. In someembodiments, the temperature during the second pumping stage may begreater than about 75° C., such as about 90° C., to facilitatesublimation of the AFS 134 and improve pumping efficiency. In someembodiments, the second pumping stage may be performed to stop theadditional etching due to the secondary etchants 138, or the secondpumping stage may be performed after the additional etching has stoppeddue to self-limiting effects. In some embodiments, the second pumpingstage may be performed a certain predetermined duration of time afterthe initial pumping stage to control the amount of additional etching.

FIGS. 11A, 11B, and 11C illustrate the formation of epitaxialsource/drain regions 82 in the first region 100A. In some embodiments,the epitaxial source/drain regions 82 are epitaxially grown in therecesses 126 using metal-organic CVD (MOCVD), molecular beam epitaxy(MBE), liquid phase epitaxy (LPE), vapor phase epitaxy (VPE), selectiveepitaxial growth (SEG), a combination thereof, or the like. Theepitaxial source/drain regions 82 may include any acceptable material,such as any material that is appropriate for n-type FinFETs. Forexample, if the fin 56 is silicon, the epitaxial source/drain regions 82may include silicon, SiC, SiCP, SiP, or the like. The epitaxialsource/drain regions 82 may have surfaces raised from respectivesurfaces of the fins 56 and may have facets. The epitaxial source/drainregions 82 are formed in the fins 56 such that each dummy gate stack 70is disposed between respective neighboring pairs of the epitaxialsource/drain regions 82. In some embodiments the epitaxial source/drainregions 82 in the first region 100A may be implanted with dopants,similar to the process previously discussed for forming the LDD regions75, followed by an anneal (see FIGS. 8A, 8B, and 8C). The epitaxialsource/drain regions 82 may have an impurity concentration of in a rangefrom about 10¹⁹ cm⁻³ to about 10²¹ cm⁻³. The n-type impurities forsource/drain regions in the first region 100A, e.g., the NMOS region,may be any of the n-type impurities previously discussed. In otherembodiments, the material of the epitaxial source/drain regions 82 maybe in situ doped during growth. In the illustrated embodiments, each ofthe source/drain regions 82 is physically separate from othersource/drain regions 82. In other embodiments, two or more adjacentsource/drain regions 82 may be merged. Such an embodiment is depicted inFIGS. 17A, 17B, and 17C, such that two adjacent source/drain regions 82are merged to form a common source/drain region. In some embodiments,more than two adjacent source/drain regions 82 may be merged.

Referring to FIGS. 12A, 12B, and 12C, after forming the epitaxialsource/drain regions 82 in the first region 100A, the epitaxialsource/drain regions 84 are formed in the second region 100B. In someembodiments, the epitaxial source/drain regions 84 are formed in thesecond region 100B using similar methods as the epitaxial source/drainregions 82 described above with reference to FIGS. 10A through 11C, andthe detailed description is not repeated for the sake of brevity. Insome embodiments, during the formation of the epitaxial source/drainregions 84 in the second region 100B, e.g., the PMOS region, the firstregion 100A, e.g., the NMOS region may be masked (not shown).Subsequently, the source/drain regions of the fins 56 in the secondregion 100B are etched to form recesses (shown as filled with theepitaxial source/drain regions 84 in FIGS. 12B and 12C) similar to therecesses 126 (See FIGS. 10A-10F). The recesses in the second region 100Bmay be formed using similar method as the recesses 126 in the firstregion, described above with reference to FIGS. 10A-10F, and thedescription is not repeated herein for the sake of brevity.

Next, the epitaxial source/drain regions 84 in the second region 100Bare epitaxially grown in the recesses using MOCVD, MBE, LPE, VPE, SEG, acombination thereof, or the like. The epitaxial source/drain regions 84may include any acceptable material, such as any material that isappropriate for p-type FinFETs. For example, if the fin 56 is silicon,the epitaxial source/drain regions 84 may comprise SiGe, SiGeB, Ge,GeSn, or the like. The epitaxial source/drain regions 84 may havesurfaces raised from respective surfaces of the fins 56 and may havefacets. In the second region 100B, epitaxial source/drain regions 84 areformed in the fins 56 such that each dummy gate 70 is disposed betweenrespective neighboring pairs of the epitaxial source/drain regions 84.In some embodiments epitaxial source/drain regions 84 may extend pastthe fins 56 and into the semiconductor strips 52.

The material of the epitaxial source/drain regions 84 in the secondregion 100B may be implanted with dopants, similar to the processpreviously discussed for forming the LDD regions 79, followed by ananneal (see FIGS. 8A, 8B, and 8C). The source/drain regions 84 may havean impurity concentration in a range from about 10¹⁹ cm⁻³ to about 10²¹cm⁻³. The p-type impurities for the source/drain regions 84 in thesecond region 100B, e.g., the PMOS region, may be any of the p-typeimpurities previously discussed. In other embodiments, the epitaxialsource/drain regions 84 may be in situ doped during growth. Portions ofthe epitaxial source/drain regions 82 and 84 that are formed near thetop surfaces 135 b of the recess 126 may have curved sidewalls orsubstantially straight sidewalls. Portions of the epitaxial source/drainregions 82 and 84 that are formed near the top surfaces 135 b of therecess 126 may physically contact the underside of the dummy dielectriclayer 58. In the illustrated embodiments, each of the source/drainregions 84 is physically separate from other source/drain regions 84. Inother embodiments, two or more adjacent source/drain regions 84 may bemerged. Such an embodiment is depicted in FIGS. 17A, 17B, and 17C, suchthat two adjacent source/drain regions 84 are merged to form a commonsource/drain region. In some embodiments, more than two adjacentsource/drain regions 84 may be merged.

The use of the additional etching of the recess to reshape the fin candecrease the width of the fin near the top of the fin more the rest ofthe fin, giving the fin a tapered, trapezoidal, or flared shape. In somecases, reshaping the fin in this manner can improve device performance.For example, it has been observed that fins having a narrower top asdescribed herein can increase the current density within the fin duringdevice operation, which can improve the I_(ON) characteristics of thedevice. In some cases, reshaping the fin as described herein may improvethe DC gain of a FinFET device by more than 1%. It has also beenobserved that fins having the shape as described herein can also reducethe amount of I_(OFF) leakage current of the device.

Referring further to FIGS. 12A, 12B, and 12C, an etch stop layer 87 andan interlayer dielectric (ILD) 88 are deposited over the dummy gatestacks 70, and over the source/drain regions 82 and 84. In anembodiment, the ILD 88 is a flowable film formed by a flowable CVD. Insome embodiments, the ILD 88 is formed of a dielectric material such asPhospho-Silicate Glass (PSG), Boro-Silicate Glass (BSG), Boron-DopedPhospho-Silicate Glass (BPSG), undoped Silicate Glass (USG), or thelike, and may be deposited by any suitable method, such as CVD, PECVD, acombination thereof, or the like. In some embodiments, the etch stoplayer 87 is used as a stop layer while patterning the ILD 88 to formopenings for subsequently formed contacts. Accordingly, a material forthe etch stop layer 87 may be chose such that the material of the etchstop layer 87 has a lower etch rate than the material of ILD 88.

Referring to FIGS. 13A, 13B, and 13C, a planarization process, such as aCMP, may be performed to level the top surface of ILD 88 with the topsurfaces of the dummy gate stacks 70. After the planarization process,top surfaces of the dummy gate stacks 70 are exposed through the ILD 88.In some embodiments, the CMP may also remove the mask 72, or portionsthereof, on the dummy gate stacks 70.

Referring to FIGS. 14A, 14B, and 14C, remaining portions of mask 72 andthe dummy gate stacks 70 are removed in an etching step(s), so thatrecesses 90 are formed. Each of the recesses 90 exposes a channel regionof a respective fin 56. Each channel region is disposed betweenneighboring pairs of the epitaxial source/drain regions 82 in the firstregion 100A or between neighboring pairs of the epitaxial source/drainregions 84 in the second region 100B. During the removal, the dummydielectric layer 58 may be used as an etch stop layer when the dummygate stacks 70 are etched. The dummy dielectric layer 58 may then beremoved after the removal of the dummy gate stacks 70.

Referring to FIGS. 15A, 15B, and 15C, gate dielectric layers 92 and 96,and gate electrodes 94 and 98 are formed for replacement gates in thefirst region 100A and the second region 100B, respectively. The gatedielectric layers 92 and 96 are deposited conformally in the recesses90, such as on the top surfaces and the sidewalls of the fins 56, onsidewalls of the gate spacers 122 and fin spacers 130, respectively, andon a top surface of the ILD 88. In some embodiments, the gate dielectriclayers 92 and 96 comprise silicon oxide, silicon nitride, or multilayersthereof. In other embodiments, the gate dielectric layers 92 and 96include a high-k dielectric material, and in these embodiments, the gatedielectric layers 92 and 96 may have a k value greater than about 7.0,and may include a metal oxide or a silicate of Hf, Al, Zr, La, Mg, Ba,Ti, Pb, and combinations thereof. The formation methods of the gatedielectric layers 92 and 96 may include Molecular-Beam Deposition (MBD),ALD, PECVD, a combination thereof, or the like.

Next, the gate electrodes 94 and 98 are deposited over the gatedielectric layers 92 and 96, respectively, and fill the remainingportions of the recesses 90. The gate electrodes 94 and 98 may be madeof a metal-containing material such as TiN, TaN, TaC, Co, Ru, Al, Ag,Au, W, Ni, Ti, Cu, combinations thereof, or multi-layers thereof. Afterthe filling of the gate electrodes 94 and 98, a planarization process,such as a CMP, may be performed to remove the excess portions of thegate dielectric layers 92 and 96, and the gate electrodes 94 and 98,which excess portions are over the top surface of ILD 88. The resultingremaining portions of material of the gate electrodes 94 and 98, and thegate dielectric layers 92 and 96 thus form replacement gates of theresulting FinFETs.

In some embodiments, the formation of the gate dielectric layers 92 and96 may occur simultaneously such that the gate dielectric layers 92 and96 are made of the same materials, and the formation of the gateelectrodes 94 and 98 may occur simultaneously such that the gateelectrodes 94 and 98 are made of the same materials. However, in otherembodiments, the gate dielectric layers 92 and 96 may be formed bydistinct processes, such that the gate dielectric layers 92 and 96 maybe made of different materials, and the gate electrodes 94 and 98 may beformed by distinct processes, such that the gate electrodes 94 and 98may be made of different materials. Various masking steps may be used tomask and expose appropriate regions when using distinct processes.

Referring to FIGS. 16A, 16B, and 16C, an ILD 102 is deposited over theILD 88, contacts 104 and 106 are formed through the ILD 102 and the ILD88, and contacts 108 and 110 are formed through the ILD 102. In anembodiment, the ILD 102 is formed using similar materials and methods asILD 88, described above with reference to FIGS. 12A, 12B, and 12C, andthe description is not repeated herein for the sake of brevity. In someembodiments, the ILD 102 and the ILD 88 are formed of a same material.In other embodiments, the ILD 102 and the ILD 88 are formed of differentmaterials.

Openings for the contacts 104 and 106 are formed through the ILDs 88 and102, and the etch stop layer 87. Openings for the contacts 108 and 110are formed through the ILD 102 and the etch stop layer 87. Theseopenings may all be formed simultaneously in a same process, or inseparate processes. The openings may be formed using acceptablephotolithography and etching techniques. A liner, such as a diffusionbarrier layer, an adhesion layer, or the like, and a conductive materialare formed in the openings. The liner may include titanium, titaniumnitride, tantalum, tantalum nitride, or the like. The conductivematerial may be copper, a copper alloy, silver, gold, tungsten,aluminum, nickel, or the like. A planarization process, such as a CMP,may be performed to remove excess materials from a top surface of theILD 102. The remaining liner and conductive material form contacts 104,106, 108, and 110 in the openings. An anneal process may be performed toform a silicide (not shown) at the interface between the epitaxialsource/drain regions 82 and 84 and the contacts 104 and 105,respectively. The contacts 104 are physically and electrically coupledto the epitaxial source/drain regions 82, the contacts 106 arephysically and electrically coupled to the epitaxial source/drainregions 84, the contact 108 is physically and electrically coupled tothe gate electrode 94, and the contact 110 is physically andelectrically coupled to the gate electrode 98. While the contacts 104and 106 are depicted in FIG. 16B in a same cross-section as the contacts108 and 110, this depiction is for purposes of illustration and in someembodiments the contacts 104 and 106 are disposed in differentcross-sections from contacts 108 and 110.

FIGS. 17A, 17B, and 17C illustrated cross-sectional views of a FinFETdevice that is similar to the FinFET device illustrated in FIGS. 16A,16B, and 16C, with like elements labeled with like numerical references.In some embodiments, the FinFET device of FIGS. 17A, 17B, and 17C may beformed using similar materials and methods and FinFET device of FIGS.16A, 16B, and 16C, described above with reference to FIGS. 1-16C, andthe description is not repeated herein for the sake of brevity. In theillustrated embodiment, two adjacent source/drain regions 82 and twoadjacent source/drain regions 84 are merged to form respective commonsource/drain regions. In other embodiments, more than two adjacentsource/drain regions 82 and more than two adjacent source/drain regions84 may be merged.

FIG. 18 is a flow diagram illustrating a method of forming a FinFETdevice in accordance with some embodiments. The method 2000 starts withstep 2001, where a substrate (such as the substrate 50 illustrated inFIG. 2A) is patterned to form strips (such as the semiconductor strips52 illustrated in FIG. 3A) as described above with reference to FIGS. 2Aand 3A. In step 2003, isolation regions (such as the isolation regions54 illustrated in FIG. 5A) are formed between adjacent strips asdescribed above with reference to FIGS. 4A and 5A. In step 2005, dummygate stacks (such as the dummy gate stacks 70 illustrated in FIGS. 7Aand 7B) are formed over the strips as described above with reference toFIGS. 6A, 6B, and 7A-7C. In step 2007, a first etching process isperformed on the strips to form recesses (such as the recesses 126illustrated in FIGS. 10A-10F) in the strips as described above withreference to FIGS. 8A-11A. In step 2009, a second etching process isperformed on the strips to form reshaped recesses (such as the recesses126 illustrated in FIG. 10F) in the strips as described above withreference to FIGS. 10C-10F. In step 2011, source/drain regions (such asthe epitaxial source/drain regions 82 illustrated in FIGS. 12B and 12C)are epitaxially grown in the reshaped recesses as described above withreference to FIGS. 11A-11C. In some embodiments, steps 2007, 2009, and2011 are performed on strips disposed in a first region of the substratewhere n-type devices are formed. In such embodiments, steps 2007, 2009,and 2011 may be repeated to be performed on strips disposed in a secondregion of the substrate where p-type devices are formed as describedabove with reference to FIGS. 12A-12C. In step 2013, replacement gatestacks (such as the gate dielectric layers 92/the gate electrodes 94 andthe gate dielectric layers 96/the gate electrodes 98 illustrated inFIGS. 15A and 15B) are formed over the strips as described above withreference to FIGS. 13A-15C.

Various embodiments discussed herein allow for improved FinFETperformance. For example, the additional etching described above withreference to FIGS. 10A-10F can shape a channel region beneath the gatestack such that the top of the channel region has a smaller lateraldimension (i.e., decreasing the surface proximity). By reducing the sizeof the top of the channel region, current flowing through the channel isconfined to a smaller volume beneath the gate stack, which can increasecurrent density during operation and improve device efficiency. Forexample, shaping the channel region as described can increase I_(ON) anddecrease I_(OFF). In some cases, reducing the surface proximity asdescribed herein can allow a strained source/drain epitaxy formed in therecess to generate greater strain near the top of the channel region,and consequently mobility near the top of the channel region can beincreased due to the strain. In some cases, increasing the depth of therecess (i.e., increasing the trench depth) next to a channel region candecrease control of the short-channel effect of the FinFET, andincreasing the diameter of the etch near the middle of the recess (i.e.,decreasing the tip proximity) can increase degradation due todrain-induced barrier leakage (DIBL). The additional etching of therecess as described herein can decrease the surface proximity withlittle or no increase of the tip proximity and with little or noincrease of the trench depth. In some cases, the embodiments describedherein can reduce the amount of residue (e.g., C, O, N, Cl, F, or othersubstances) remaining on etched surfaces.

According to an embodiment, a method includes forming a fin over asubstrate, forming an isolation region adjacent the fin, forming a dummygate structure over the fin, recessing the fin adjacent the dummy gatestructure to form a first recess using a first etching process,reshaping the first recess to form a reshaped first recess using asecond etching process, wherein the second etching process etches upperportions of the fin adjacent the top of the recess more than the secondetching process etches lower portions of the fin adjacent the bottom ofthe recess, and epitaxially growing a source/drain region in thereshaped first recess. Reshaping the first recess includes performing anoxide etch process, wherein the oxide etch process forms a porousmaterial layer within the recess. The porous material layer includesammonium fluorosilicate (AFS). The oxide etch process includes a plasmaetch. Reshaping the first recess includes removing portions of theporous material layer, wherein a greater amount of the porous materiallayer adjacent the bottom of the recess is removed than the amount ofporous material layer adjacent the top of the recess while removingportions of the porous material layer. The second etching process isperformed in the same chamber as the oxide etching process. The reshapedfirst recess is widest at the top of the reshaped first recess. Thesecond etching process includes etching using radicals. Epitaxiallygrowing the source/drain region in the reshaped first recess includesepitaxially growing a first semiconductor material in the reshaped firstrecess, the first semiconductor material being different from a secondsemiconductor material of the fin.

According to another embodiment, a method includes patterning asubstrate to form a strip, the strip including a first semiconductormaterial, forming an isolation region along a sidewall of the strip, anupper portion of the strip extending above a top surface of theisolation region, forming a dummy gate structure along sidewalls and atop surface of the upper portion of the strip, a first etching processon an exposed portion of the upper portion of the strip to form a firstrecess, the exposed portion of the strip being exposed by the dummy gatestructure, forming a porous material covering portions of the firstsemiconductor material of the sidewalls of the first recess, etching thefirst semiconductor material of the sidewalls of the first recess,wherein first portions of the first semiconductor material of thesidewalls of the first recess that are covered by more porous materialare etched more than second portions of the first semiconductor materialof the sidewalls of the first recess that are covered by less porousmaterial, thereby reshaping the first recess, and epitaxially growing asource/drain region in the reshaped first recess. The first portions ofthe first semiconductor material of the sidewalls of the first recessare closer to the top of the first recess than the second portions ofthe first semiconductor material of the sidewalls of the first recess.The porous material includes ammonium fluorosilicate (AFS). The methodincludes removing the porous material. Etching the first semiconductormaterial of the sidewalls of the first recess includes chemicallyetching the first semiconductor material using radicals. Etching thefirst semiconductor material of the sidewalls of the first recessincludes chemically etching the first semiconductor material usingammonium hydroxide (NH₄OH). The method includes removing an oxide fromthe sidewalls of the first recess using an oxide etch process that isdifferent than the first etching process.

According to another embodiment, a device includes a fin over asubstrate, wherein the fin is narrower at a top surface of the fin thanbelow the top surface of the fin, wherein the fin has a first sidewallslope at the top of the fin and a second sidewall slope at the bottom ofthe fin, and wherein the fin has a third sidewall slope between thefirst sidewall slope and the second sidewall slope that is greater thanthe first sidewall slope and that is greater than the second sidewallslope, an isolation region adjacent the fin, a gate structure alongsidewalls of the fin and over the top surface of the fin, a gate spacerlaterally adjacent the gate structure, and an epitaxial region adjacentthe fin, wherein a first portion of the epitaxial region adjacent thetop surface of the fin protrudes beneath the gate spacer a greaterlateral distance than a second portion of the epitaxial region below thetop surface of the fin. The first portion of the epitaxial region hasstraight sidewalls. The epitaxial region is wider at the top surface ofthe fin than below the top surface of the fin. The fin includes a firstsemiconductor material and the epitaxial region includes a secondsemiconductor material, the second semiconductor material beingdifferent from the first semiconductor material.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming a fin over asubstrate; forming an isolation region adjacent the fin; forming a dummygate structure over the fin; recessing the fin adjacent the dummy gatestructure to form a first recess using a first etching process;reshaping the first recess to form a reshaped first recess using asecond etching process, wherein the second etching process etches upperportions of the fin adjacent the top of the recess more than the secondetching process etches lower portions of the fin adjacent the bottom ofthe recess, wherein reshaping the first recess comprises performing anoxide etch process, wherein the oxide etch process forms a porousmaterial layer within the recess; and epitaxially growing a source/drainregion in the reshaped first recess.
 2. The method of claim 1, whereinthe porous material layer comprises ammonium fluorosilicate (AFS). 3.The method of claim 1, wherein the oxide etch process comprises a plasmaetch.
 4. The method of claim 1, wherein reshaping the first recesscomprises removing portions of the porous material layer, wherein agreater amount of the porous material layer adjacent the bottom of therecess is removed than the amount of porous material layer adjacent thetop of the recess while removing portions of the porous material layer.5. The method of claim 1, wherein the second etching process isperformed in the same chamber as the oxide etching process.
 6. Themethod of claim 1, wherein the reshaped first recess is widest at thetop of the reshaped first recess.
 7. The method of claim 1, wherein thesecond etching process comprises etching using radicals.
 8. The methodof claim 1, wherein epitaxially growing the source/drain region in thereshaped first recess comprises epitaxially growing a firstsemiconductor material in the reshaped first recess, the firstsemiconductor material being different from a second semiconductormaterial of the fin.
 9. A method comprising: patterning a substrate toform a strip, the strip comprising a first semiconductor material;forming an isolation region along a sidewall of the strip, an upperportion of the strip extending above a top surface of the isolationregion; forming a dummy gate structure along sidewalls and a top surfaceof the upper portion of the strip; performing a first etching process onan exposed portion of the upper portion of the strip to form a firstrecess, the exposed portion of the strip being exposed by the dummy gatestructure; forming a porous material covering portions of the firstsemiconductor material of the sidewalls of the first recess; etching thefirst semiconductor material of the sidewalls of the first recess,wherein first portions of the first semiconductor material of thesidewalls of the first recess that are covered by more porous materialare etched more than second portions of the first semiconductor materialof the sidewalls of the first recess that are covered by less porousmaterial, thereby reshaping the first recess; and epitaxially growing asource/drain region in the reshaped first recess.
 10. The method ofclaim 9, wherein the first portions of the first semiconductor materialof the sidewalls of the first recess are closer to the top of the firstrecess than the second portions of the first semiconductor material ofthe sidewalls of the first recess.
 11. The method of claim 9, whereinthe porous material comprises ammonium fluorosilicate (AFS).
 12. Themethod of claim 9, further comprising removing the porous material. 13.The method of claim 9, wherein etching the first semiconductor materialof the sidewalls of the first recess comprises chemically etching thefirst semiconductor material using radicals.
 14. The method of claim 9,wherein etching the first semiconductor material of the sidewalls of thefirst recess comprises chemically etching the first semiconductormaterial using ammonium hydroxide (NH₄OH).
 15. The method of claim 9,further comprising removing an oxide from the sidewalls of the firstrecess using an oxide etch process that is different than the firstetching process.
 16. A method comprising: forming a strip protrudingfrom a semiconductor substrate; forming an isolation region adjacent thestrip; recessing the isolation region to expose an upper portion of thestrip; forming a dummy gate structure along sidewalls and a top surfaceof the upper portion of the strip; performing a plasma etching processon the upper portion of the strip to form a recess adjacent the dummygate structure; performing surface modification process on surfaces ofthe recess, the surface modification process forming a porous materialwithin the recess; performing a first pumping process to remove firstportions of the porous material from the recess, wherein second portionsof the porous material remaining within the recess comprise etchants;and etching surfaces of the recess using the etchants.
 17. The method ofclaim 16, further comprising after etching surfaces of the recess usingthe etchants, performing a second pumping process to remove the secondportions of the porous material remaining within the recess.
 18. Themethod of claim 16, wherein surfaces of the recess proximate the top ofthe recess are etched more than surfaces of the recess proximate thebottom of the recess.
 19. The method of claim 16, wherein the surfacemodification process comprises a plasma etch process.
 20. The method ofclaim 16, wherein the surface modification process removes oxide fromthe surfaces of the recess.